Polymeric coated metal strip and method for producing same

Abstract

The present invention is a process for continuous extrusion coating the surfaces of a metal strip which includes the steps of moving said metal strip by means of a plurality of rolls. The strip then has impinged on its first and second surfaces to be coated an oxidizing flame. The first surface passes through a corona discharge and extruded on to the first surface is a melted polymeric extrudiate. Thereafter, the surface is passed over a chill roll having a temperature less than said extrudiate to provide a first coated surface. The second surface is then subjected to a oxidizing flame and corona discharge and a melted polymeric extrudiate is extruded on to the second surface. Thereafter, the second surface is passed over a chill roll having a temperature less than said extrudiate to provide a second coated surface. The coated strip is then reheated to about the melt temperature of said extrudiates and quenched to provide an extrusion coated strip of the present invention.

What is claimed is:  
     
         1 . A process for continuous extrusion coating one of the surfaces of a metal strip comprising the steps of: 
 a) moving said strip by means of a plurality of rolls;    b) impinging at least one of said surfaces to be coated with an oxidizing flame only or an oxidizing flame followed by a Corona discharge;    c) extruding on to said impinged surface of said moving strip a melted polymer extrudate and then passing said surface over a chill roll having a temperature less than said extrudate to provide a first coated surface;    d) reheating said moving strip having a first coated surface to about the melting temperature of said extrudate; and    e) quenching said reheated strip.    
     
     
         2 . A process for continuous extrusion coating both surfaces of metal strip comprising the steps of: 
 a) moving said metal strip by means of a plurality of rolls;    b) impinging at least one of said surfaces to be coated with an oxidizing flame only or an oxidizing flame followed by a Corona discharge;    c) extruding on to said impinged surface of said moving strip a melted polymer extrudate and therefore passing said surface over a chill roll having a temperature less than said extrudate to provide a first coated surface;    d) subjecting said non-coated surface to a second oxidizing flame treatment only, a Corona discharge treatment only, or an oxidizing flame treatment followed by a Corona discharge;    e) extruding onto said non-coated surface of said moving strip a melted polymer extrudate and therefore passing said surface over a second chill roll having a temperature less than said extrudate to provide a second coated surface;    f) reheating said moving strip having a first and second coated surface to about the melt temperature of said extrudate; and    g) quenching said reheated strip.    
     
     
         3 . A process for continuous extrusion coating the surfaces of a metal strip comprising the steps of: 
 a) moving said metal strip by means of a plurality of rolls;    b) impinging on the first and second surfaces to be coated an oxidizing flame;    c) passing a first surface through a Corona discharge;    d) extruding on to a first surface a melted polymer extrudate and therefore passing said surface over a chill roll having a temperature less than said extrudate to provide a first coated surface;    e) subjecting said second surface to an oxidizing flame treatment only, a Corona discharge treatment only, or an oxidizing flame followed by a Corona discharge;    f) extruding on to said second surface a melted polymer extrudate and therefore passing said surface over a second chill roll having a temperature less than said extrudate to provide a second coated surface;    g) reheating said moving strip having a first and second coated surface to about the melt temperature of said extrudates; and    h) quenching said reheated strip to provide an extrusion coated strip.    
     
     
         4 . A process as set forth in    claim 1   ,    2   , or  3  wherein said moving strip is between about 150 ft/min. to 1500 ft/min.  
     
     
         5 . A process as set forth in    claim 1   ,    2   , or  3  wherein the polymer is heated to a temperature necessary for extrusion coating and said chill rolls are maintained between about 100° F. and 190° F.  
     
     
         6 . A process as set forth in    claim 1   ,    2   , or  3  wherein the melted polymer film exiting the die lip is positioned from 24″ and 6″ above the moving strip/chill roll interface with the melt being applied to the moving strip at a position just prior to contact of the coated metal surface with the chill roll surface.  
     
     
         7 . A process as set forth in    claim 1   ,    2   , or  3  wherein the nip roll consists of neoprene or steel applied by pressure against a chill roll.  
     
     
         8 . A process as set forth in    claim 1   ,    2   , or  3  wherein the moving strip is initially pre-treated using a flame with a plasma value between 30 and 50 plasma units and positioned at approximately 90° to the moving metal strip such that the cones of the flame just touch the strip surface.  
     
     
         9 . A process as set forth in    claim 1   ,    2   , or  3  wherein initial flame pre-treatment is followed by a second pre-treatment consisting of a Corona discharge operated in a range between 5 to about 30 watts/ft 2 /min.  
     
     
         10 . A process as set forth in    claim 1   ,    2   , or  3  wherein the coated metal strip exiting the chill roll/striper roll is post-treated by re-melting the coating in by heating the strip to a temperature between 265° F. to about 550° F., a delay before quench of from 1 second to 5 seconds, and a laminar flow water quench at a temperature ranging from 35° F. to about 120° F.  
     
     
         11 . A process as set forth in    claim 1   ,    2   , or  3  wherein the metal strip to be coated is selected from the group consisting of electrolytic tinplate, electro-coated chromium steel, electro-coated galvanize steel, hot-dip galvanized steel (HDG), blackplate, cold rolled steel strip, aluminum coated steel, all types of stainless steels, hot rolled strip, Galvalume coated steel and nonferrous metal strip.  
     
     
         12 . A process as set forth in    claim 1   ,    2    or  3  wherein said melted polymer of coating extrudate or co-extrudate of at least one polymer selected from the group comprises at least one layer and adhesion consisting of polypropylene, copolymers of polypropylene, polyethylene, copolymers of polyethylene terephthalate, copolymers, polybutylene terephthalate blends of polypropylene, polyethylene, polybutylene homopolymer polyethylene and polybutylene random copolymer, nylon, copolymers of nylon and optionally an adhesive admixed with such selected polymer.  
     
     
         13 . A process as set forth in    claim 12    wherein said layer includes one or more colorant pigments, nucleators, antimicrobial additive, and friction modifier.  
     
     
         14 . A polymer coated metal strip having an extruded or co-extruded polymeric coating with a total thickness from about 0.3 to 15.0 mils, a high modulus of bending, and can be drawn or ironed wherein the adhesion of said coating is sufficiently good such that the coating does not delaminate during such operations.  
     
     
         15 . A polymer coated metal strip as set forth in    claim 13    wherein the metal strip is as set forth on    claim 11    and the polymer coating consists of at least one extruded polymer layer.  
     
     
         16 . A polymer coated metal strip as set forth in    claim 13    wherein a first layer comprises a blend of polypropylene homopolymer with a grafted maleic anhydride polypropylene component.  
     
     
         17 . A polymer coated metal strip as set forth in    claim 13    wherein a bulk layer is selected from at least one of the group and consists of primarily polypropylene homopolymer, polypropylene random copolymer, a blend of polypropylene homopolymer and polypropylene random copolymer, polyamides, EVOH, and polyethylene terephthalate.  
     
     
         18 . A polymer coated metal strip as set forth in    claim 13    wherein at top layer consists of polypropylene homopolymer and polypropylene random copolymer combined with polymeric components having at least one chemical and physical property to provide hardness, scuff/scratch resistance, brittleness, stain resistance, or UV resistance to said top layer.  
     
     
         19 . A process as set forth in    claim 1   ,    2   , or  3  wherein the coated metal has the polymer surface of said strip treated, for instance by corona discharge to enhance post decoration quality.  
     
     
         20 . A process as set forth in    claim 1   ,    2    or  3  wherein said extruded film is an extrudable material or a blend of extrudable materials selected from the group consisting of polypropylene, polybutylene terephthalate, polyethylene terephthalate, polyethylene, polyester, nylon (polyamide-PA), ethlene copolymers, such as ethylene vinyl acetate and ethylene n-butyl acrylate, vinyl acetate, normal butyl acrylate and polyvinylidene chloride